The inherent notion of solar furnaces, wind-powered machines and a combination of the two, are well known and there is a substantial body of prior art in each category.
Solar Furnaces
Solar furnaces intensify light through the use of either a point focus lens or a parabolic mirror. At the point of focus, a liquid is introduced through appropriate methods and is brought to the boiling point and transferred via a conduit to a steam engine. This steam engine, in turn, will create power to drive an electrical generator. Such systems suffer from a number of design problems that heretofore limited their effectiveness and utility.
Point focus systems must be precisely aligned to track the sun, and therefore require expensive mechanical sun-pointing systems to be effective. Parabolic mirrors suffer from the same alignment problems. These systems tend to be delicate in construction and susceptible to wind--which can cause system misalignment and therefore decreased system efficiency. High winds can also damage a solar powered system (mostly circular or parabolic mirrors) which limits the size of the systems, and therefore can only be located in areas that have high solar radiations and low wind intensity. Solar furnaces also suffer from reduced efficiency when the sky is overcast and obviously offer no utility at night.
Circular or parabolic mirrors are limited to diameters of under eight feet because of potential wind damage. Another problem related to such systems is that they must have vast areas of land to operate efficiently and to create economies of scale.
There have been many attempts to overcome these limitations by redesigning the system to be less environmentally sensitive and to dispense with sun-tracking mechanisms. One way to overcome these limitations is by using a spherical collector--of which there are number in the prior art.
U.S. Pat. No. 4,056,093 by Barger discloses a spherical solar heater. The disclosed design consists of two concentrically mounted and sealed hemispheres. Water, or another liquid, is heated at the bottom of the space between the two hemispheres, and the heated liquid is released at the top.
U.S. Pat. No. by 4,404,961 by Stuhlman discloses an apparatus for collecting solar energy. This design utilizes a hemisphere to heat fluids. The assembly is designed to rotate to follow the sun. The design places a heating tube away from the axis of rotation.
U.S. Pat. No. 4,043,315 by Cooper discloses a solar heat collector having a transparent, spherical outer shell and an inner shell with a plurality of magnifying lenses. The system does not rotate on any axis.
U.S. Pat. No. 4,047,385 by Brinjevec discloses a spherical boiler assembly that has plurality of magnifying lenses mounted above it. Again, there is no rotational component to the system.
None of these patents accommodate any mode of generating supplemental power from the wind. They do, however, validate the efficacy of using a spherical boiler assembly to produce steam in the present invention.
Wind Machines
Wind machines come in a variety of shapes and with varying degrees of efficiency. These systems can be loosely classified as either rotor powered or vortex generators. Rotor-powered systems include, but are not limited to, the Savonius, Darius, wind turbine, Magnus or Flettner Rotors, and horizontal-blade systems. There are also exists in the prior art, spherical wind machines.
U.S Pat. Nos. 4,012,163 by Baumgartner and 4,115,032 by Lange both disclose wind driven generators that are spherical in construction. These designs utilize a plurality of blades to generate useable power. Both systems are mounted on a vertical axis, and therefore, are subject to the Magnus effect.
The Magnus effect subjects such vertical structures to a lift component that is perpendicular to the direction of the wind. While this effect allows the rotor to turn it also causes severe torsional load problems as the system is scaled up. This is discussed in some detail below.
Both confined and unconfined vortex generators spin the wind to increase the power output of the system. Such systems utilize the potential or pressure energy of the wind. It is estimated that such systems can be designed to provide up to six times the power output of conventional wind machines with the same rotor diameter.
However, unconfined vortex generators require shrouds or ducts that add to the complexity and weight of the system to such a degree as to make such systems operationally impractical. And confined vortex generators require large tower-like structures to contain the vortex. These structures are expected to have heights three times the diameter of the tower or nine times the diameter of the turbine. Such structures are necessary due to the fact the system would require the natural flow of air in sufficient quantities to create practical power. U.S. Pat. Nos. 4,07,131 and 4,935,639 both represent forms of vortex generators.
Hybrid Solar/Wind Systems
U.S. Pat. Nos. 4,433,544 by Weils; 4,224,528 by Argo; 4,575,639 by Rogow; 4,779,006 by Worthham; 4,551,631 by Trigilio; 4,369,629 by Lockwood; and 4,229,941 by Hope all disclose systems that utilize both wind and solar power.
U.S. Pat. Nos. 4,433,544 by Weils; 4,224,528 by Argo; and 4,779,006 by Worthham all employ methods of heating ambient air to power a turbine--which in turn drives a generator. The Weils and Argo patents utilize clear panels to raise the temperature of the ambient air. The Wortham patent heats the ambient air using a mirrored surface. None of these disclosed patents utilizes a solar boiler assembly to actively drive the turbine.
U.S. Pat. Nos. 4,575,639 by Rogow; 4,551,631 by Trigilio; 4,369,629 by Lockwood utilize both wind and solar power. However, the solar power is not derived from either the heating of the ambient air nor use of a solar boiler. Rather, these systems use photovoltaic cells by simply adding them onto a wind powered turbine. Therefore, these inventions do not have a direct relation to the present invention.
U.S. Pat. No. 4,229,941 by Hope discloses a system that is claimed to be capable of generating energy from solar and wind energy sources. The system embodies a parabolic mirror to capture sunlight; a mirror assembly and fresnel lens to intensify this sunlight; and a boiler to convert the resultant heat into mechanical energy. There is also a bladed wind rotor attached to the output shaft of the boiler to garner additional energy from the wind. The system consists of two separate assemblies, one for the parabolic mirror (solar furnace) and the other for the solar boiler and wind rotor. The two assemblies are connected through a fresnel tube that is used to transmit light from the parabolic assembly to the solar boiler. The inherently delicate design of the system requires a high degree of precision in manufacturing and is susceptible to damage by high winds.
The Hope system seems susceptible to damage under high winds due to the torsional loads placed on the vertical shaft of the boiler and wind rotor assembly. It is well known that high winds impart translational force perpendicular to direction of the wind on objects of cylindrical cross-section. This translational force will cause the solar boiler to twist. This twisting motion could cause the tubular fresnel lens assembly to become misaligned and diminish the efficiency of the system. These deficiencies could be partially overcome by the use of very high strength materials, which in turn would raise the cost of the system.
But even such additions would not alleviate certain other deficiencies of the design. First, the co-location of the two assemblies creates a number of design compromises. If these assemblies are located closely together--the wind rotor would be obstructed from direct access to the prevailing wind, if the wind is blowing in the direction behind that of the solar assembly. If in turn, the solar assembly is moved to some distance away from the boiler assembly, the fresnel tube would have to be elongated-- which accentuates problems related to the twisting motion of the wind (and subsequent misalignment) that was previously discussed because the rigidity of the tube would be compromised. In addition, the fresnel tube, like all light carrying media would be subject to decreased efficiency due to loss of light intensity caused by the distance the light would have to be conveyed.
The system would also be difficult to scale-up. It is well known that wind power increases as a function of the cube of the surface area of the rotor. Therefore, all the previously discussed translational forces placed on the assemblies would be magnified as the system was enlarged to create more power. Furthermore, there are practical considerations as locating this system at a suitable site.
Wind efficiency increases as a function of height. Therefore, it is desirous to place wind machines on elevating structures to increase efficiency. To elevate the Hope system would require either placing both assemblies on top of one structure or building two structures--one for each assembly. The former choice would create the wind blockage of the rotor of the solar assembly, as previously discussed. The latter choice would require two separate structures--adding to the cost of the system and creating difficult problems of designing a fresnel tube with sufficient rigidity to span the distance between the two towers.
Furthermore, this system also requires a solar tracking mechanism to refract light into the solar boiler, which adds to complexity and systems costs. The costs and complexity of such solar tracking methods have been one of the mitigating factors against the adoption of solar energy systems.